X-ray systems have been used for years as the primary method for bone and cartilage detection. The penetrating nature of X-rays and their variable absorption based on the density of the material make them good candidates for “seeing inside” the parts to be inspected. While X-rays seem to be an ideal solution for inspection within poultry processing facilities, the qualities of chicken breasts and their structural relationship between bone and cartilage make X-ray alone an inadequate tool for properly identifying bones and cartilage.
X-rays can simply be described as electromagnetic energy that penetrates objects and experiences absorption or transmission based on the atomic mass of the object. Unfortunately, it is very difficult for X-ray images to distinguish between a thin slice of dense material and a thicker slice of less dense material. This means that thin bones will show the same gray level on an X-ray scan as thick meat. In these situations, the shape of the foreign object must be analyzed because the grayscale level is an inadequate indicator of atomic mass.
Object shape, however, is not a clear indicator of the presence of bones or cartilage. Chicken breasts will usually have a smooth outer surface and an inner surface with irregularities such as folded meat parts and fat pieces. Unfortunately, folded meat pieces and other object characteristics on the underside of the breast cannot generally be distinguished from bones or cartilage, either in shape or in color. X-ray systems that utilize both shape and color will do a reasonable job of identifying foreign material, but the accuracy rates will not allow their use in a fully automated, unattended mode.
There have been countless movies with scenes that show law enforcement officials reviewing surveillance video where the character asks the computer operator to “enhance the image.” Undoubtedly, the computer operator will be able to recover striking details from a base image that clearly did not contain this detail from the start. These scenes, unfortunately, are only possible in the movies.
The poultry industry (as well as other industries that rely on hidden object detection) has been attempting similar impossible decision making with imagery that does not contain enough information with which to make the decision. Standard, unaided X-ray imagery simply does not provide the amount of information needed to make accurate bone and cartilage detection decisions.
Even though great strides have been made in processing software to squeeze every ounce of information out of X-ray imagery, it becomes necessary in production systems to increase the quality of the information supplied to the software. Several attempts have been made to increase image quality for inspection and foreign object detection.
U.S. Pat. No. 6,023,497 discloses a single X-ray emitter with a tuned detector and U.S. Pat. No. 5,585,603 describes how to use a single emitter X-ray device for determining the weight of an object. Furthermore, U.S. Pat. No. 6,299,524 describes a single X-ray system used to determine bone fractures. Other single emitter functionality is disclosed in U.S. Pat. Nos. 6,512,812, 6,546,071 and 6,563,904.
Some increased functionality has been gained by using more than one detector for a single X-ray emitter. Specifically, U.S. Pat. No. 5,757,878 discloses a single emitter with a plurality of detectors, while U.S. Pat. No. 5,428,657 describes a single X-ray emitter system that analyzes Rayleigh and Compton scattering.
Better detection of unwanted objects has been realized by utilizing a second X-ray emitter. U.S. Pat. No. 6,600,805 describes the use of two X-ray sources, each emitting different energies, and two detectors. U.S. Pat. No. 6,370,223 builds on this concept by defining two X-ray sources, each emitting different energies, with the use of laser profilometry to determine object thickness and factor the thickness out of the X-ray imagery. U.S. Pat. Nos. 6,449,334 and 6,597,759 utilize two X-ray sources, each emitting different energies, and two detectors along with the analysis of Compton scattering.
Computed tomography (CT) systems advanced the state of the art in X-ray scanning by utilizing multiple views of a “slice” of an object. The CT systems typically include an X-ray emitter and an array of X-ray detectors connected on diametrically opposite sides of the annular disk, with the disk being mounted within a gantry support. During the scan of an object located within the opening of the disk, the disk rotates about an axis while the X-rays pass from the focal spot of the fan-shaped beam from the emitter through the inspected object to the detectors. The X-ray emitter and detector array are positioned so that X-ray paths between the focal spot and each detector all lie in the same plane (herein referred to as the “slice plane”), which is orthogonal to the travel axis of the part under inspection.
CT technology creates cross-sectional slices of an object by rotating the X-ray emitter and detector 360 degrees around the object. A cross-section is created from all of the images gathered, which are typically taken at one-degree increments for each cross section. The object under inspection is then advanced an incremental amount and the 360 degrees scan is performed again. By moving the specimen incrementally through the system and obtaining a 360 degrees slice at each increment a precise 3-D computer model of the object can be created.
U.S. Pat. No. 6,597,761 describes a single emitter CT for processing logs, while U.S. Pat. No. 5,818,897 discloses a single emitter CT with a two-dimensional array of detectors. U.S. Pat. Nos. 5,182,764, 6,430,255 and 6,590,956 all describe aspects of a single emitter CT with a single-stage X-ray pre-scan.
Several patents describe systems with CT capabilities, but with single rotational emitters replaced with multi-emitter configurations. U.S. Pat. No. 6,018,562 claims a multi-emitter configuration where the emitters and detectors are configured in L-shaped arrays. U.S. Pat. Nos. 6,088,423 and 6,236,709 disclose three-emitter systems used for baggage inspection. U.S. Pat. No. 6,453,000 claims a five-emitter system with partially overlapping X-ray beams.
These CT systems can construct somewhat accurate 3-D computer models of heterogeneous solids by stitching the contiguous slices together to form the representation of the object. If rotational and multi-emitter CT systems were fast enough, their use in meat, poultry, fish, fruit, vegetable, grain and baked goods processing facilities would allow very reliable foreign object detection with minimal false positives. For example, because poultry processing facilities must process birds at rates from 20 to 1000 birds per minute, the use of conventional CT systems for full inspection of boneless chicken pieces is not practical. Given the small size of bones and cartilage in meat products, the lack of accuracy of these CT-like systems is problematic.
There is the need for a system that can obtain the detection accuracy of CT systems, but at fast enough rates and with the required accuracy to be used for full, automated inspection of specimens in production facilities.